Light-Activated Hydrogel Repairs Cartilage

BALTIMORE, Jan. 15, 2013 — Runners and knee pain sufferers, take heed. A new squishy biomaterial called a hydrogel could help repair damaged cartilage when activated with light, giving those achy joints some relief.

The Johns Hopkins University hydrogel scaffolding, when implanted into the holes in injured cartilage, can jump-start cartilage growth while discouraging cells from making scar tissue, according to results from a 15-patient study. The proof-of-concept study suggests that the light-activated hydrogel could be a versatile, safe way to enhance traditional cartilage repair, and could pave the way for larger trials of the biomaterial’s safety and effectiveness, the tissue engineers said.

“Our pilot study indicates that the new implant works as well in patients as it does in the lab, so we hope it will become a routine part of care and improve healing,” said Dr. Jennifer Elisseeff, Jules Stein Professor of Ophthalmology and director of the Johns Hopkins University School of Medicine’s Translational Tissue Engineering Center.

Damage to cartilage, the tough-yet-flexible material that gives shape to ears and noses and lines the surfaces of joints so they can move easily, can be caused by injury, disease or faulty genes.

Clinical procedure for adhesive-hydrogel implantation into a cartilage defect developed by tissue engineers at Johns Hopkins University. Both schematics and actual patient images are shown for the final steps. (A) A mini-incision approach was created to expose the cartilage defect. The defect edges were debrided to remove any dead tissue at the cartilage edge. (B) The adhesive was applied to the base and walls of the defect, followed by surgical microfracture. (C) Last, the hydrogel solution was injected into the defect and photopolymerized in situ with light. (D) Bleeding from the microfracture holes was trapped in and around the hydrogel. Courtesy of Science Translational Medicine/AAAS.
Microfracture — a surgery in which tiny holes are punched in a bone near the injured cartilage to stimulate a person’s stem cells to emerge from bone marrow and grow new cartilage atop the bone — is the standard of care for cartilage repair, but for holes in cartilage caused by injury, the procedure often either fails to stimulate new cartilage growth or grows cartilage that is less hardy than the original tissue.

Elisseeff and colleagues theorized that the specialized stem cells needed a nourishing scaffold on which to grow, but demonstrating the clinical value of hydrogels has “taken a lot of time,” she said. By experimenting with various materials, her group eventually developed a promising hydrogel, and then an adhesive that could bind it to the bone.

The hydrogel is first poured into the cartilage hole as a viscous liquid. Shining light on the biomaterial solidifies it and starts a tissue growth-promoting action.

When the hydrogel and adhesive were tested on 15 patients with holes in their knee cartilage as part of the first clinical study, MRIs showed that these patients had new cartilage filling an average of 86 percent of the defect in their knees after six months. Control patients treated with only the microfracture surgery had an average of 64 percent of the tissue replaced. Patients with the hydrogel implant also reported a greater decrease in knee pain, the investigators said.

The trial is continuing with more enrolled patients; it is now being managed by Biomet Inc. of Warsaw, Ind., a manufacturer of products used by musculoskeletal medical specialists for surgical and nonsurgical therapy.

Elisseeff and her team are now working to develop a next-generation implant in which the hydrogel and adhesive will be combined in a single material. They also are working on technologies to lubricate joints and reduce inflammation.